Apparatus for handling objects

ABSTRACT

Apparatus for handling objects is provided with controls to automatically regulate fluid pressure in a fluid-operated hoist under certain conditions. The apparatus includes a fluid-operated hoist, fluid-operated, object-engaging means, and responsive means sensitive to the pressure of the fluid of the objectengaging means to change the pressure of the fluid supplied to the hoist. In a preferred embodiment, the object-engaging means is embodied in a headlight aiming instrument which adjusts the headlights of automobiles on an assembly line. The aiming instrument includes a vacuum cup constituting the object-engaging means, which is affixed to the lens of the headlight. The instrument then adjusts the aim of the headlight to a predetermined position automatically. Since the weight of the instrument itself is accommodated in the adjustment, the hoist is controlled to balance the weight of the instrument until the vacuum cup is engaged with the headlight. At that time, the responsive means will lower the pressure in the hoist to just balance the cable and the connector which attaches the cable to the instrument. This leaves the full weight of the instrument itself unbalanced, as if no hoist were present. As soon as the vacuum is released, through the responsive means the pressure in the hoist is raised to balance the weight of the instrument in addition to the cable and connector. The invention can also be applied to fixtures having fluid-operated object-engaging means. When an object is engaged by the engaging means, the pressure in the hoist can be automatically raised to equal or exceed the weight of the object, in addition to the fixture, the engaging means, and the cable, to raise the object or enable an operator to raise it. All of the pressure changes are accomplished without any manipulation by the operator being required.

United States Patent 1 Stone APPARATUS FOR HANDLING OBJECTS [75] Inventor: Charles W. Stone, Garden City,

Mich.

[73] Assignee: D. W. Zimmerman Mfg., Inc.,

Madison Heights, Mich.

[22] Filed: Dec. 1, 1971 [211 Appl. No.: 203,646

[52] US. Cl. 254/168, 254/186 R, 294/64 R [51] Int. Cl B66d 1/44 [58] Field of Search 254/168, 186 R; 294/64 R, 65, 64 A, 64 B; 214/1 BS, 1 BT, l BH; 192/3 R [56] References Cited UNlTED STATES PATENTS 2,874,989 2/1959 Reynolds 294/64 R 3,457,837 7/1969 Powell 254/186 R 2,801,760 8/1957 Christofierson 254/168 X 3,372,822 3/1968 Weinert 294/64 R 2,831,554 4/1958 Reynolds 192/3 R Primary Examiner-Richard E. Aegerter Assistant Examiner-Merle F. Maffei AttorneyAllen D. Gutchess, Jr.

[57] ABSTRACT Apparatus for handling objects is provided with controls to automatically regulate fluid pressure in a fluidoperated hoist under certain conditions. The apparatus 1 Sept. 4, 1973 includes a fluid-operated hoist, fluid-operated, objectengaging means, and responsive means sensitive to the pressure of the fluid of the object-engaging means to change the pressure of the fluid supplied to the hoist. In a preferred embodiment, the object-engaging means is embodied in a headlight aiming instrument which adjusts the headlights of automobiles on an assembly line. Y

The aiming instrument includes a vacuum cup constituting the object-engaging means, which is affixed to the lens of the headlight. The instrument then adjusts the aim of the headlight to a predetermined position automatically. Since the weight of the instrument itself is accommodated in the adjustment, the hoist is controlled to balance the weight of the instrument until the vacuum cup is engaged with the headlight. At that time, the responsive means will lower the pressure in the hoist to just balance the cable and the connector which attaches the cable to the instrument. This leaves the full weight of the instrument itself unbalanced, as if no hoist were present. As soon as the vacuum is released, through the responsive means the pressure in the hoist is raised to balance the weight of the instrument in addition to the cable and connector. The invention can also be applied to fixtures having fluid-operated objectengaging means. When an object is engaged by the engaging means, the pressure in the hoist can be automatically raised to equal or exceed the weight of the object, in addition to the fixture, the engaging means, and the cable, to raise the object or enable an operator to raise it. All of the pressure changes are accomplished without any manipulation by the operator being required.

11 Claims, 5 Drawing Figures PATENTEDsEP 4am 3.756.563 sum 1 OF 2 FIGZ INVENTOR. I CHARLES WSTONE ATTOR NEY 1 APPARATUS FOR HANDLING OBJECTS This invention relates to apparatus for handling objects and particularly such apparatus with controls for automatically changing the pressure in a hoist of the apparatus as fluid-operated, object-engaging means associated therewith is engaged with or disengaged from an object.

Basically, the invention enables a fluid-operated hoist to handle an object with minimum manual control by an operator being required. By way of a specific example, the invention embodies an instrument or device for automatically aiming headlights in a new automobile on an assembly line. The instrument employs a vacuum cup to engage the lens of the headlight, with the headlight then being adjusted to a predetermined position through the instrument and a computer associated therewith. The weight of the instrument is included in the calculations made by the computer. Consequently, any hoist used with the instrument must not have any effect on the weight of the instrument, when in operation. However, since the instrument is expensive, sensitive, and delicate, a hoist is extremely desirable to assure that the instrument will not fall when the vacuum cup is released from the headlight lens.

In accordance with the invention, the aiming instrument is connected through a cable to an overhead, fluid-operated hoist. The hoist includes a pressure regulator through which hoist pressure is controlled, with the regulator in turn being controlled by pilot fluid pressure. A pressure-responsive valve is used to control the pilot fluid pressure, with the valve being responsive to the pressure in the vacuum cup of the instrument. When the vacuum is high or the absolute pressure is low, as occurs when the vacuum cup is attached to the headlight lens, the pressure-responsive valve vents pilot fluid from the regulator to lower the pilot pressure and lower the pressure of the fluid supplied through the regulator to the hoist. This venting is adjusted so that the hoist is effective only to balance the weight of a hoist cable and the connector which connects the hoist cable to the headlight aiming instrument. When the headlight adjustment is complete and fluid is supplied to the vacuum cup to separate the instrument from the lens, it must be assured that the instrument cannot fall. Accordingly, the responsive valve, upon sensing .the loss of vacuum, stops the venting and thereby raises the pilot control pressure to raise the pressure of fluid supplied through the regulator to the hoist sufficiently to balance the weight of the instrument, thereby to prevent any possibility of it falling.

Another embodiment of the invention can be used in an object-handling system in which objects are engaged and picked up with the aid of a hoist. A pressureresponsive valve automatically places the hoist under higher pressure when a fluid-operated, object-engaging means of a fixture is engaged with the object. In a specific example, the responsive valve senses the pressure in a fluid-operated clamping cylinder and causes the pressure in the hoist to increase when a clamp or jaw operated by the cylinder engages the object. Again, no separate operation of the hoist controls is required on behalf of the operator, the operator merely manipulating and actuating the fixture.

It is, therefore, a principle object of the invention to provide a hoist with controls for automatically changing the hoist pressure when an object is engaged.

Another object of the invention is to provide a hoist for automatically balancing an instrument when disengaged from an object, to prevent the possibility of the instrument falling.

A further object of the invention is to provide a hoist with a fixture having fluid-operated, object-engaging means with controls for increasing pressure in the hoist when an object'is engaged.

Other objects and advantages of the invention will be apparent from the following detailed description of preferred embodiments thereof, reference being made to the accompanying drawings, in which:

FIG. 1 is a somewhat schematic view in perspective, with parts broken away, of a hoist, an instrument with an object-engaging means, and controls, in accordance with the invention;

FIG. 2 is a diagrammatic view of certain hoist controls of FIG. 1;

FIG. 3 is a somewhat schematic view in cross-section of a pressure-responsive valve constituting part of the controls of the apparatus of FIGS. 1 & 2;

FIG. 4 is a diagrammatic view, with parts in section of a modification of the invention, including a hoist, a fixture with a fluid-operated, object-engaging means, and controls therefor; and

FIG. 5 is a somewhat schematic view in cross section of a pressure-responsive valve consitituting part of the controls of FIG. 4.

Referring now to the drawings and specifically FIG. 1, a pneumatically-operated hoist with which the invention can be used is indicated at 10. The hoist shown is of the type disclosed in U. S. Pat. No. 3,260,508, although other fluid-operated hoists can also be used advantageously with the invention. The hoist 10 includes a power chamber 12 at one end thereof to which fluid, commonly air, is supplied under pressure. A piston 14 forms one end of the chamber 12 and is adjacent a rotatable drum 16 on which a flexible member or cable 18 is carried. When air under sufficient pressure is supplied to the chamber 12, it forces the piston 14 toward the opposite end of the hoist and moves the cable drum 16 in the same direction. The drum 16 is supported on a ball-screw assembly (not shown) which causes the drum to rotate as it moves longitudinally thereof in the hoist 10, the drum rotating in a direction to raise the cable 18. When the pressure in the chamber 12 is sufficiently low, the weight of the load carried by the cable 18 will cause the drum 16 to rotate in the opposite direction, in a direction to lower the cable 18 and at the same time to move the piston 14, along with the drum 16, toward the chamber end of the hoist. Hence, when the air pressure in the hoist chamber 12 is sufficient, it causes the cable 18 to raise any object carried by the cable and when the pressure is sufficiently low, the cable and object are lowered. The pressure in the chamber 12 can also be adjusted to a predetermined value sufficient to just balance the weight of the object to enable the operator to manipulate the object up and down, as if it had practically no weight.

The air pressure in the chamber 12 is controlled through a regulator control 20, which is preferably of the pilot air-control type, as shown in U. S. Pat. No. 3,457,837.

The cable 18 is connected by a loop or other suitable connector 22 to a fluid-operated, object-engaging device or vacuum cup indicated as 24. In this instance, the device 24 is part of a headlight aiming instrument 26 which adjusts the headlights of automobiles on an assembly line. The instrument 26 is a commerciallyavailable unit, the details of which do not constitute part of the invention. The vacuum cup 24 is affixed to the lens of a headlight 28 mounted in a fender 30 of an automobile proceeding along an assembly line. With the vacuum cup in place, the instrument 26, in combination with a computer 32 with which it is connected by conrol cables 34, assures that the headlight is properly aimed. The instrument 26 is extremely sensitive and its own weight is built into the calculation made by the computer 32 through signals received through the cables 34 from the instrument. Because the instrument is also delicate and expensive, considerable care must be taken to assure that it cannot fall when disengaged from the headlight 28. Accordingly, the hoist is automatically controlled so that when the vacuum cup 24 is engaged with the lens of the headlight 28, the pressure in the hoist chamber 12 is reduced to the point that the hoist just balances the cable 18 and the connector 22 so that the effective weight of the instrument 26 is the same as if no hoist were connected to it at all. However, when the vacuum cup 24 is disengaged from the headlight, air under higher pressure is immediately supplied to the chamber 12 to cause the hoist to also balance the weight of the instrument 26, preventing the possibility of it falling.

A venturi tube 36 (FIG. 2) is built into the instrument '26 with a line 38 connecting the throat of the venturi with the vacuum cup 24 and specifically with a central rigid back plate 40 thereof, the vacuum cup also having an annular flexible flange 42. Air is supplied to the venturi tube 36 through a line 44 and a valve 46 which is also built into the instrument 26. The valve has a control button 48 which directs air from a supply line 50 either through the line 44 or through a blow-off line 52 which also communicates with the acuum cup 24 through the back plate 40. When air is supplied through the line 44, the low pressure established at the throat of the venturi 36 establishes a vacuum in the cup 24. When the air is diverted through the line 52, it destroys the vacuum and enables the vacuum cup 24 to be quickly separated from or blown off of the lens of the headlight 28. A check valve can be located in the line 38 to prevent vacuum established in the vacuum cup 24 from being lost in the event of failure of the air supplied through the lines 44 and 50. This is discussed more fully in US. Pat. No. 3,423,119.

A pressure-responsive valve 54 is connected through a line 56 and the line 52 to the vacuum cup 24. The valve 54 also is connected through a line 58 with the pressure regulator control 20. Through the combination of the control 20 and the valve 54, the pressure in the hoist chamber 12 is regulated automatically. When the vacuum cup 24 is not engaged with the object and specifically the lens of the headlight 28, the pressure in the cup is substantially atmospheric or ambient. The valve 54 is then in a blocking position and air under higher pressure, as regulated by the control 20, is supplied to the chamber 12. This pressure is sufficient to at least offset the weight of the instrument 26, the connector 22 and the cable 18 so that the instrument cannot fall. When the vacuum cup 24 is engaged with the object and specifically the lens of the headlight 28, a vacuum is established in the vacuum cup 24 which is transmitted through the line 56 to the valve 54. The valve then shifts to cause venting of air through the line 58 from the control 20, with the control then supplying air under lower pressure to the chamber 12. The pres sure then is just sufficient to offset the weight of the cable 18 and the connector 22, along with the line 56, so that the instrument 26 then functions the same as if the hoist and its related components were not present.

The operation of the controls to achieve the above results will now be discussed in more detail. The control 20 includes a main regulator 60 which controls the pressure of the air supplied from a supply line 62 through a filter 64 and through a passage 66 to the chamber 12. The pressure of the air controlled by the main regulator 60 is determined by a pilot aircontrolled regulator 68 which receives air from the supply line 62 and supplies it through a passage 70 past a flow-control valve 72 to a bonnet chamber 74 of the main regulator. The pressure in the bonnet chamber 74 controls the pressure output of the main regulator 60 with the pressure of this chamber controlled by the pilot-controlled regulator 68 which can be adjusted through an adjusting screw 76. The pressure in the bonnet chamber 74 controls the pressure output of the main regulator 60 with the pressure of this chamber controlled by the pilot-controlled regulator 68 which can be adjusted through an adjusting screw 76. The pressure in the bonnet chamber 74 also is controlled through the valve 54. When this valve is in a venting position, the chamber pressure is lower than otherwise when the valve is in a blocking position. Thus, the hoist chamber 12 is at higher pressure when the valve 54 is blocking and is at a lower pressure when the valve 54 is venting.

A suitable design for the pressure-responsive valve 54 is shown more particularly in FIG. 3. The valve 54 includes a valve body 78 having a central bore 80 in which is a sealing cylinder 82 having appropriately placed O-ring seals 84 to contain air passing therethrough. A spool valve 86 is located in a central passage 88 in the cylinder 82 and includes a sealing piston 90 at one end and an enlargement 92, to serve as a guide, at the other end. a coil spring 94 is in engagement with the end of the sealing piston 90 and urges'the spool valve toward an upper block position. An inlet 98 communicates with the line 58 and an outlet 100 communicates with a vent line 102; a recess 104 receives a fitting 106 for the line 56. The inlet 98 and the outlet 100 communicate with the central passage 88 through ports 108 and 110 in the cylinder 82. Communication between the ports 108 and 110 is prevented by the cylinder 90 of the spool valve 86 when the spool valve is urged upwardly to the upper position by the spring 94. However, when a sufficient vacuum is established in the vacuum cup 24, this is communicated through the line 56 to the lower end of the pressure-responsive valve 54. This vacuum moves the spool valve 86 downwardly against the force of the spring 94, so that air from the line 58 can be vented through the line 102 around a small intermediate portion 112 of the spool valve 86. In this position, the bonnet chamber 74 of the main regulator 60 is vented through the line 102 and the main regulator 60 thus supplies air under lower pressure to the passage 66 and the chamber 12.

Through the adjusting screw 76 of the pilot regulator 68 and through adjustment of the flow control valve 72, the lower pressure in the chamber 12 can be of a value just sufficient to overcome the weight of the hoist components connected to the instrument 26 to enable the the hoist chamber 12. This hoist pressure is adjusted to be sufficient to overcome the weight of the instrument 26 as well as the cable and connector.

Modified load handling apparatus embodying the invention is shown in FIGS. 4 & 5. Here the same hoist can be employed or other fluid-operated hoists can be used, with fluid pressure again controlled by the regulator control 20. The flexible member or cable 18 is connected by a loop 1 14, in this instance, to a modified load-engaging fixture 115. The fixture 115 includes a frame 116 having a fluid-operated, load-engaging device or means 118, including a stationary jaw 120 and a movable jaw 122 which can engage and release an object or load 124. The jaw 122 is affixed to an end of a piston rod 124 connected to a piston 126 in a fluidoperated cylinder 128 which is also affixed to the frame 118 and is part of the engaging means 118. Fluid, such as air, for the cylinder 128 can be supplied by a branch line 130 communicating with the supply line 62, and a four-way valve 132. From here, the air can be supplied to the blind end of the cylinder 128 through a line 134 and to the rod end of the cylinder through lines 136 and 138.

A line 140 also is connected with the rod end of the cylinder 128 through the line 138, with the line 140 communicating with a pressure-responsive valve 142. This valve is connected through a line 144 with the bonnet chamber 74 of the regulator control 20, the interior of the control 20 not being shown again in FIG.

The valve 142 is shown in more detail in FIG. 5. The valve includes a valve body 146 having a central bore 148 in which a sealing cylinder 150 is located, the cylinder having suitably placed O-rings 152 to prevent air leakage. A spool valve 154 is located in a central passage 156 in the cylinder 150 and includes a sealing piston 158 at one end and an enlargement 160 which serves at the other end as a guide. A coil spring 162 is in engagement with the end of the piston 158 and urges the spool valve 154 toward a lower, blocking position. An inlet 164 in the valve body 146 communicates with the line 144 and an outlet 166 in the body 146 communicates with a vent line 168 with a recess 170 in the lower end of the valve body receiving a fitting 172 for the line 140. The inlet 164 and the outlet 166 communicate with the central passage 156 of the cylinder 150 through ports 174 and 176. Communication between the ports 174 and 176 is prevented by the sealing cylindcr 158 when the spool valve 154 is urged downwardly to the lower position by the spring 162. However, when sufficient pressure is established in the rod end of the cylinder 128, this is communicated through the line 140 to the lower end of the pressure-responsive valve 142. This pressure moves the spool valve 154 upwardly against the force of the spring 162, so that air from the line 144 can then be vented through the line 168 around a small intermediate portion 178 of the spool valve 154. This lowers the pressure in the bonnet chamber of the control 20 and reduces the pressure supplied to the power chamber 12 of the hoist 10 so that the hoist balances only the cable, the connector, and the fixture when the object 124 is released.

When an object is to be engaged once again, the object-engaging means 118 is operated. Accordingly, air is supplied through the valve 132 and the line 134 to the blind end of the cylinder 128, causing the piston 126 to move toward the object 124 and to move the jaw 122 into engagement with the object. At the same time, the rod end of the cylinder 128 is vented through the valve 132 so that pressure in the line similarly drops. The spring 162 then moves the spool valve 154 downwardly once again to block the line 144 and enable the control 20 to again supply air at higher pressure to the hoist 10. This pressure is adjusted so that the weight of the fixture 115 and the object 124 is balanced or slightly exceeded, depending on whether it is desired to have the hoist raise the object 124 or just balance it so that an operator can manipulate it as desired. In either case, the desired pressure change is achieved without the necessity for the operator to manipulate any hoist controls at all.

Various modifications of the above described embodiments of the invention will be apparent to those skilled in the art and it is to be understood that such modifications can be made without departing from the scope of the invention, if they are within the spirit and the tenor of the accompanying claims.

I claim:

1. Apparatus for handling an object comprising a pneumatically-operated hoist having a housing, drum means movable in said housing, elongate flexible means connected to said drum means, a power' chamber formed in said housing, piston means effective to move the drum means in the housing when fluid under sufficient pressure is supplied to said chamber, a pressure regulator for controlling pressure of fluid supplied to said housing, fluid-responsive control means for controlling said pressure regulator, fluid-operated engaging means for engaging an object, said engaging means being carried by said flexible means, means for supplying fluid to said engaging means, the fluid for said engaging means being under one pressure when an object is engaged and being under another pressure when the object is disengaged, means communicating the pressure of said fluid-operated engaging means to said fluid-responsive-control means, said fluid-responsive means causing said pressure regulator to supply fluid under one pressure to said power chamber when the fluid pressure of said fluid-operated engaging means is at said one pressure, and said fluid-responsive control means causing said pressure regulator to supply fluid under another pressure to said power chamber when the fluid pressure of said fluid-operated engaging means is at said another pressure.

2. Apparatus according toclaim 1 characterized by said one pressure of said engaging means being less than atmospheric pressure and said another pressure of said engaging means being higher than said one pressure.

3. Apparatus according to claim 1 characterized by said another pressure to said power chamber being sufficient to balance said fluid-operated engaging means.

4. Apparatus according to claim 1 characterized by said one pressure to said power chamber being insufficient to balance the weight of said fluid-operated engaging means.

5. Apparatus according to claim 1 characterized by said fluid-responsive control means comprising a fluidresponsive valve, said valve having a venting position for venting fluid from said pressure regulator when said fluid-operated engaging means is at said one pressure, and said valve having a blocking position not venting fluid from said pressure regulator when said fluidoperated engaging means is at said another pressure.

6. Apparatus according to claim 1 characterized by said fluid-responsive control means comprising a fluidresponsive valve, said valve having a blocking position to prevent venting of fluid from said pressure regulator when said fluid-operated engaging means is at said one pressure, and said valve having a venting position for venting fluid from said pressure regulator when said fluid-operated engaging means is at said another pressure.

7. Apparatus for handling an object comprising a pneumatically-operated hoist having a housing, a drum movable in said housing, a power chamber formed within said housing, piston means effective to move said drum in one direction in the housing when fluid under sufficient pressure is supplied to said chamber, elongate flexible means connected to said drum, fluidoperated engaging means for engaging an object, means for connecting said engaging means and said flexible means, a fluid-controlled pressure regulator for controlling pressure of fluid supplied to said chamber, fluid-operated control means for regulating control fluid for said pressure regulator, means for communicating fluid pressure of said fluid-operated engaging means to said fluid-operated control means, said fluidoperated control means causing said pressure regulator to supply fluid under one pressure to said chamber when said fluid-operated engaging means is engaged with an object, said fluid-operated control means causing said pressure regulator to supply fluid under another pressure to said chamber when said fluidoperated engaging means is disengaged from the object.

8. Apparatus according to claim 7 characterized by said one pressure to said chamber being sufficient to offset the weight of said elongate flexible means and said another pressure to said chamber being sufiicient to at least off set the weight of said elongate-flexible means and said fluid-operated engaging means.

9. Apparatus according to claim 7 characterized by said one pressure to said chamber being sufficient to enable the hoist to offset the weight of said elongate flexible means, said fluid-operated engaging device, and an engaged object, and said another pressure to said chamber being sufficient to enable the hoist to offset the weight of said elongate flexible means, and said fluid-operated engaging means.

10. Apparatus according to claim 7 characterized by said fluid-operated control means comprising a fluidresponsive valve having a venting position and a blocking position.

11. Apparatus according to claim 10 characterized by said fluid-controlled pressure regulator having a bonnet chamber influencing the output of the pressure regulator, said fluid-responsive valve being in communication with said bonnet chamber. 

1. Apparatus for handling an object comprising a pneumaticallyoperated hoist having a housing, drum means movable in said housing, elongate flexible means connected to said drum means, a power chamber formed in said housing, piston means effective to move the drum means in the housing when fluid under sufficient pressure is supplied to said chamber, a pressure regulator for controlling pressure of fluid supplied to said housing, fluidresponsive control means for controlling said pressure regulator, fluid-operated engaging means for engaging an object, said engaging means being carried by said flexible means, means for supplying fluid to said engaging means, the fluid for said engaging means being under one pressure when an object is engaged and being under another pressure when the object is disengaged, means communicating the pressure of said fluid-operated engaging means to said fluid-responsive control means, said fluidresponsive means causing said pressure regulator to supply fluid under one pressure to said power chamber when the fluid pressure of said fluid-operated engaging means is at said one pressure, and said fluid-responsive control means causing said pressure regulator to supply fluid under another pressure to said power chamber when the fluid pressure of said fluid-operated engaging means is at said another pressure.
 2. Apparatus according to claim 1 characterized by said one pressure of said engaging means being less than atmospheric pressure and said another pressure of said engaging means being higher than said one pressure.
 3. Apparatus according to claim 1 characterized by said another pressure to said power chamber being sufficient to balance said fluid-operated engaging means.
 4. Apparatus according to claim 1 characterized by said one pressure to said power chamber being insufficient to balance the weight of said fluid-operated engaging means.
 5. Apparatus according to claim 1 characterized by said fluid-responsive control means comprising a fluid-responsive valve, said valve having a venting position for venting fluid from said pressure regulator when said fluid-operated engaging means is at said one pressure, and said valve having a blocking position not venting fluid from said pressure regulator when said fluid-operated engaging means is at said another pressure.
 6. Apparatus according to claim 1 characterized by said fluid-responsive control means comprising a fluid-responsive valve, said valve having a blocking position to prevent venting of fluid from said pressure regulator when said fluid-operated engaging means is at said one pressure, and said valve having a venting position for venting fluid from said pressure regulator when said fluid-operated engaging means is at said another pressure.
 7. Apparatus for handling an object comprising a pneumatically-operated hoist having a housing, a drum movable in said housing, a power chamber formed within said housing, piston means effective to move said drum in one direction in the housing when fluid under sufficient pressure is supplied to said chamber, elongate flexible means connected to said drum, fluid-operated engaging means for engaging an object, means for connecting said engaging means and said flexible means, a fluid-controlled pressure regulator for controlling pressure of fluid supplied to said chamber, fluid-operated control means for regulating control fluid for said pressure regulator, means for communicating fluid pressure of said fluid-operated engaging means to said fluid-operated control means, said fluid-operated control means causing said pressure regulator to supply fluid under one pressure to said chamber when said fluid-operated engaging means is engaged with an object, said fluid-operated control means causing said pressure regulator to supply fluid under another pressure to said chamber when said fluid-operated engaging means is disengaged from the object.
 8. Apparatus according to claim 7 characterized by said one pressure to said chamber being sufficient to offset the weight of said elongate flexible means and said another pressure to said chamber being sufficient to at least off set the weight of said elongate-flexible means and said fluid-operated engaging means.
 9. Apparatus according to claim 7 characterized by said one pressure to said chamber being sufficient to enable the hoist to offset the weight of said elongate flexible means, said fluid-operated engaging device, and an engaged object, and said another pressure to said chamber being sufficient to enable the hoist to offset the weight of said elongate flexible means, and said fluid-operated engaging means.
 10. Apparatus according to claim 7 characterized by said fluid-operated control means comprising a fluid-responsive valve having a venting position and a blocking position.
 11. Apparatus according to claim 10 characterized by said fluid-controlled pressure regulator having a bonnet chamber influencing the output of the pressure regulator, said fluid-responsive valve being in communication with said bonnet chamber. 